1. Field of the Invention
The present invention relates to a process for manufacturing flexible or low density polyurethane foams. In particular, the present invention relates to a process for manufacturing polyurethane foams with improved wet compression set properties, firmness, resilience and elongation, without using fluorocarbons as auxiliary blowing agents. The invention also provide processes for manufacturing flexible polyurethane foams with density of up to 45 kg/m.sup.3, preferably from 15 to 45 kg/m.sup.3.
The flexible polyurethane foams produced by the process of the present invention can be used as seat cushioning material for vehicles, aircraft, furniture and the like.
2. Background of the Invention
In conventional processes for manufacturing flexible polyurethane foams having density of 45 kg/m.sup.3 or less employing water without low boiling point fluorocarbons, for example, Fron 11 and Fron 123 which destroys ozone layers, as auxiliary blowing agents, a greater deal of water has needed to be used on an equal foaming magnification basis. Polyurethane foams obtained thus possessed lowered resilience property and increased wet compression set property.
To improve these drawbacks, processes of, as a member of polyols, using ethylene oxide adducts of tetraols are disclosed in Japanese unexamined application No. 75021/1988 and those of using ethylene oxide adducts of di- or tri-functional starter compounds are proposed in EP 367283.
However, polyurethane foams produced by the former processes have lowered elongation property and those by the latter processes have insufficient firmness in spite of being improved in wet compression set and elongation properties.
Inventors of the present invention examined relations of type and structure of a starter compound with amount of ethylene oxide to be added to the compound and found the followings.
(1) Starter compounds having hydroxyl groups of 4 or more provide polyurethane foams with lowered elongation property. PA1 (2) Starter compounds having hydroxyl groups of 2 or less provide polyurethane foams with lowered firmness. PA1 (3) Ethylene oxide adducts of trimethylol propane and those of glycerin having no secondary hydroxyl group are easy to provide, because of great reactivity of these adducts with polyisocyanates due to primary hydroxyl groups incorporated therein, polyurethane foams with closed-cell structure or insufficient wet compression set improvement. PA1 (a) a polyol having a hydroxyl equivalent of from 800 to 10,000, PA1 (b1) a first glycerin derivative of the formula: ##STR1## where n and m are zero or an integer such that the sum of n and m ranges from 1 to 8, or PA1 (b2) a mixture of the first glycerin derivative and a second glycerin derivative of the formula: ##STR2## where p and r are zero or an integer, q is an integer of 1 or more such that the sum of p, q and r ranges from 1 to 8, and PA1 (c) water,
In consideration of these findings, inventors of the present invention created a process for making flexible polyurethane foams having increased firmness and resilience properties without significant worsening of wet compression set and elongation property by using combinations of high molecular weight polyols with specified hydroxyl equivalent, ethylene oxide adducts of glycerin with a secondary hydroxyl group and water as a blowing agent.